Vehicle Navigation System and Method

ABSTRACT

An efficient route-defining method includes determining a route to a destination. The exemplary method also includes determining a wireless device to server connection type and assigning a tolerance in accordance with a connection type. The tolerance is usable to determine if a vehicle is off-route, and the tolerance is increased or decreased inversely corresponding to the speed of the connection type. According to the illustrative method, the assigned tolerance is used to determine points defining the route, such that the roads comprising the route are within a bounded area. The bounded area may be defined by the tolerance in conjunction with a plurality of lines connecting successive points along the route. Finally, the method includes delivering the determined points to a vehicle computing system in communication with the server.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 12/847,650filed Jul. 30, 2010, which disclosure of which is incorporated in itsentirety by reference herein. This application further relates to U.S.application Ser. No. 13/463,167, filed May 3, 2012.

BACKGROUND

Vehicle navigations systems, such as on-board systems and portable GPSsystems, have been available for years now. Originally, theses systemswould often receive map information from removable media, such as a CDor DVD. More recently, many of the map systems have an internal memorystoring map information.

Although some systems store maps on local memory, such as a hard diskdrive (HDD) or flash memory, other systems may contact a remote networkto receive mapping information. This information, for example, may be aseries of directions delivered over a wireless connection. In instancessuch as this, where map data is not stored (or only partially stored) ona local HDD, a provider may be constrained by, for example, bandwidthlimitations, in how quickly the data can be delivered.

In at least one existing system, the Ford SYNC system, a vehiclecomputing system (which may contain or is in communication with avehicle navigation system, either on or off-board) may connect to aremote network using the voice channel. This connection is a limitedbandwidth connection employing the voice-band of a wireless deviceconnected to the vehicle computing system and a remote network.

Because the voice-band has a limited available bandwidth, information iscapped at a low delivery speed (relative to, for example, a pure dataconnection). While this normally may not affect a need-for-datascenario, because the user can wait, in some instances this can besomewhat problematic, as in the case of a user in a moving vehiclerequesting directions. If the requested directions cannot be deliveredin an efficient manner over the available bandwidth, then the user mayactually pass a first or even a second turn on a route before thedirections are delivered to the vehicle (due, for example, to a largefile being delivered over a low bandwidth connection).

SUMMARY

In a first illustrative embodiment, a method includes determining aroute to a destination. The exemplary method also includes determining awireless device to server connection type and assigning a tolerance inaccordance with the connection type. The tolerance is usable todetermine if a vehicle is off-route, and the tolerance is increased ordecreased inversely corresponding to the speed of the connection type.In other words, for a fast connection, the tolerance is low (meaning amore precise route, likely having more route points and a greater datasize, but also having an increased likelihood of swift off-routecondition detection.

According to the illustrative method, the assigned tolerance is used todetermine points defining the route, such that the roads comprising theroute are within a bounded area. The bounded area may be defined by thetolerance in conjunction with a plurality of lines connecting successivepoints along the route.

Finally, the method includes delivering the determined points to avehicle computing system in communication with the server.

In a second illustrative embodiment, method includes determining a routeto a destination and determining a road classification for each road ora portion of each road comprising the route. In one non-limitingexample, road classifications are based on speed ranges.

The exemplary method also includes assigning a tolerance to each road orportion of each road based on the determined classification for thatroad or road portion.

The method further includes determining points defining the route, usingthe assigned tolerances, such that the roads comprising the route arewithin a bounded area defined by the tolerance in conjunction with aplurality of lines connecting successive points along the route.Finally, the method includes delivering the determined points to avehicle computing system in communication with the server.

In yet a third illustrative embodiment, a server-implemented methodincludes determining a route to a destination and dividing the routeinto a plurality of portions. The method also includes determining anumber of exits for each portion and assigning a tolerance to eachportion based on the determined number of exits.

The illustrative method also includes determining points defining theroute, using the assigned tolerances, such that the roads comprising theroute are within a bounded area defined by the tolerance in conjunctionwith a plurality of lines connecting successive points along the route.

Finally, the method includes delivering the determined points to avehicle computing system in communication with the server.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example block topology for a vehicle basedcomputing system;

FIG. 2 shows an illustrative example of a route to be traveled;

FIG. 3 shows an illustrative example of a navigation calculation with alow off-route threshold overlaid on the route shown in FIG. 2;

FIG. 4 shows an illustrative example of a navigation calculation with adynamically adjustable off-route threshold, overlaid on the route shownin FIG. 2;

FIG. 5 shows an illustrative example of a process for adjusting athreshold based on a road classification;

FIG. 6 shows an illustrative example of a process for dynamicallyadjusting an off-route threshold based on a likelihood of an off-routeoccurrence; and

FIG. 7 shows an illustrative example of a process for determining alikelihood of an off-route occurrence.

DETAILED DESCRIPTION

FIG. 1 illustrates an example block topology for a vehicle basedcomputing system 1 (VCS) for a vehicle 31. An example of such avehicle-based computing system 1 is the SYNC system manufactured by THEFORD MOTOR COMPANY. A vehicle enabled with a vehicle-based computingsystem may contain a visual front end interface 4 located in thevehicle. The user may also be able to interact with the interface if itis provided, for example, with a touch sensitive screen. In anotherillustrative embodiment, the interaction occurs through, button presses,audible speech and speech synthesis.

In the illustrative embodiment 1 shown in FIG. 1, a processor 3 controlsat least some portion of the operation of the vehicle-based computingsystem. Provided within the vehicle, the processor allows onboardprocessing of commands and routines. Further, the processor is connectedto both non-persistent 5 and persistent storage 7. In this illustrativeembodiment, the non-persistent storage is random access memory (RAM) andthe persistent storage is a hard disk drive (HDD) or flash memory.

The processor is also provided with a number of different inputsallowing the user to interface with the processor. In this illustrativeembodiment, a microphone 29, an auxiliary input 25 (for input 33), a USBinput 23, a GPS input 24 and a BLUETOOTH input 15 are all provided. Aninput selector 51 is also provided, to allow a user to swap betweenvarious inputs. Input to both the microphone and the auxiliary connectoris converted from analog to digital by a converter 27 before beingpassed to the processor.

Outputs to the system can include, but are not limited to, a visualdisplay 4 and a speaker 13 or stereo system output. The speaker isconnected to an amplifier 11 and receives its signal from the processor3 through a digital-to-analog converter 9. Output can also be made to aremote BLUETOOTH device such as PND 54 or a USB device such as vehiclenavigation device 60 along the bi-directional data streams shown at 19and 21 respectively.

In one illustrative embodiment, the system 1 uses the BLUETOOTHtransceiver 15 to communicate 17 with a user's nomadic device 53 (e.g.,cell phone, smart phone, PDA, or any other device having wireless remotenetwork connectivity). The nomadic device can then be used tocommunicate 59 with a network 61 outside the vehicle 31 through, forexample, communication 55 with a cellular tower 57. In some embodiments,tower 57 may be a WiFi access point.

Exemplary communication between the nomadic device and the BLUETOOTHtransceiver is represented by signal 14.

Pairing a nomadic device 53 and the BLUETOOTH transceiver 15 can beinstructed through a button 52 or similar input. Accordingly, the CPU isinstructed that the onboard BLUETOOTH transceiver will be paired with aBLUETOOTH transceiver in a nomadic device.

Data may be communicated between CPU 3 and network 61 utilizing, forexample, a data-plan, data over voice, or DTMF tones associated withnomadic device 53. Alternatively, it may be desirable to include anonboard modem 63 having antenna 18 in order to communicate 16 databetween CPU 3 and network 61 over the voice band. The nomadic device 53can then be used to communicate 59 with a network 61 outside the vehicle31 through, for example, communication 55 with a cellular tower 57. Insome embodiments, the modem 63 may establish communication 20 with thetower 57 for communicating with network 61. As a non-limiting example,modem 63 may be a USB cellular modem and communication 20 may becellular communication.

In one illustrative embodiment, the processor is provided with anoperating system including an API to communicate with modem applicationsoftware. The modem application software may access an embedded moduleor firmware on the BLUETOOTH transceiver to complete wirelesscommunication with a remote BLUETOOTH transceiver (such as that found ina nomadic device).

In another embodiment, nomadic device 53 includes a modem for voice bandor broadband data communication. In the data-over-voice embodiment, atechnique known as frequency division multiplexing may be implementedwhen the owner of the nomadic device can talk over the device while datais being transferred. At other times, when the owner is not using thedevice, the data transfer can use the whole bandwidth (300 Hz to 3.4 kHzin one example).

If the user has a data-plan associated with the nomadic device, it ispossible that the data-plan allows for broad-band transmission and thesystem could use a much wider bandwidth (speeding up data transfer). Instill another embodiment, nomadic device 53 is replaced with a cellularcommunication device (not shown) that is installed to vehicle 31. In yetanother embodiment, the ND 53 may be a wireless local area network (LAN)device capable of communication over, for example (and withoutlimitation), an 802.11g network (i.e., WiFi) or a WiMax network.

In one embodiment, incoming data can be passed through the nomadicdevice via a data-over-voice or data-plan, through the onboard BLUETOOTHtransceiver and into the vehicle's internal processor 3. In the case ofcertain temporary data, for example, the data can be stored on the HDDor other storage media 7 until such time as the data is no longerneeded.

Additional sources that may interface with the vehicle include apersonal navigation device 54, having, for example, a USB connection 56and/or an antenna 58; or a vehicle navigation device 60, having a USB 62or other connection, an onboard GPS device 24, or remote navigationsystem (not shown) having connectivity to network 61.

Further, the CPU could be in communication with a variety of otherauxiliary devices 65. These devices can be connected through a wireless67 or wired 69 connection. Also, or alternatively, the CPU could beconnected to a vehicle based wireless router 73, using for example aWiF±71 transceiver. This could allow the CPU to connect to remotenetworks in range of the local router 73. Auxiliary device 65 mayinclude, but are not limited to, personal media players, wireless healthdevices, portable computers, and the like.

FIG. 2 shows an illustrative example of a route to be traveled. In thisillustrative embodiment, a user is first located at a present location201. The user may currently be in motion or be stationary, but this isthe point from which the directions to a destination 215 are requested.

In this embodiment, a first road 203, along which a user is traveling,is relatively straight. Even though the road curves north as it travelseast, the road is generally straight and has no off-roads before theuser turns onto road 205.

Road 205 has several switchbacks, but is also free of intersectionsbefore the user enters road 207. Road 207 is taken to road 213 whichleads to the destination. Road 207 has a rather significant curve in it,as well as several off-roads 209 and 211 which the user must bypass inorder to reach destination 215.

FIG. 3 shows an illustrative example of a navigation calculation with alow off-route threshold overlaid on the route shown in FIG. 2. In thisillustrative embodiment, a navigation system has a low off-routethreshold 301. The off-route threshold is a tolerance that determines ifa user is still traveling on an assigned route. For example, withoutlimitation, if the tolerance is set at twenty feet (20 ft), then as longas a GPS position of a user is detected within twenty feet of the GPScoordinates corresponding to a given road, the navigation system willrecognize that the user is still traveling on the proper route.

If the off-route tolerance is set too high for a given area, a usercould be well off route and the system would not recognize the off-routecondition. For example, without limitation, if a the tolerance were setat two hundred feet, in a neighborhood where streets were one hundredfeet apart, then the user could be off-route by as much as two streetsand the navigation system would still think the user was on route.

In the illustrative embodiment shown in FIG. 3, the tolerance 301 isshown bordering the route to be traveled (the actual roads have beenremoved for clarity of illustration). The route 317 is the route “known”by the navigation system. In this embodiment, as long as the actual roadremains within the tolerance around the route 317, additional “routepoints” (e.g., 303) are only necessary as long as fewer route pointswould provide a route that exists outside the tolerance. In other words,because the tolerance contains the entire actual route, then as long asthe user remains on the actual route, the system will not register anoff-route condition. If the user accidentally turned and ended up atposition 319, then an off-route condition would be recognized.

As can be seen in FIG. 3, for at least the first portion of travel tooff-route point 319, the road is still within the tolerance, so it maytake a few seconds for the system to recognize the off-route condition.If the tolerance were made smaller, then more of the road leading tooff-route point 319 would fall outside the tolerance and the systemwould recognize the off-route condition sooner. The tradeoff in this,however, is that more road points may be needed to define the route, asareas such as the curve between points 309 and 311 and the curve betweenpoints 321 and 313. With the tolerance at its present level, however,the entire route remains within the tolerance, and thus, as long as thedriver remains on the route, the system will not register an off-routecondition.

In this illustrative embodiment, fifteen points are used to represent aroute. Each point can be at least a two part number pair, each numberhaving six decimal places. Thus, using a low tolerance, a long route ora route with many turns may require a significant number of data pointsto define.

In this embodiment, the route 317 is represented by a series of straightlines connecting the route points. These straight lines are not theactual lines along which a user will travel, but serve to define thetolerance within which the actual route may be contained.

In this illustrative embodiment, a route point is included at least ateach turn. On the route between points 201, 303 and the first of points305, it may be possible to define the route using only points 201 andthe first of points 305. This, however, would not include the turn atpoint 303, and the user would be left to guess which direction to takewhen the road forked. At each data point, however, the system canprovide an instruction if needed, and thus the system can include theinstruction to turn at point 303.

In some instances, a series of points may be needed to define a portionof a route, even though no instruction may be provided at those points.For example, without limitation, points 305 and 307 define the turns atthose points, although no actual instruction to the user is needed(since the user has no option but to follow the road. The need for theplurality of points defining the turn could be removed by increasing thetolerance, although this could cause other problems, as previously noted(such as a failure to recognize an off-route condition quickly enough).Similarly, points 311, 315 would not be needed if the tolerance wereincreased.

Points 309, 313 and 321 are included because there are road breaksand/or turn instructions required at those points.

FIG. 4 shows an illustrative example of a navigation calculation with adynamically adjustable off-route threshold, overlaid on the route shownin FIG. 2. In this illustrative embodiment, a larger threshold may beused for portions of the route 415 where there is little or no chance ofthe user going off-route. For example, between points 201 and 407, thereis only one turn-off where a user could go off route (after point 401),accordingly, in this embodiment, the off-route threshold is set at alarge value (for example, 100 feet). Since the user would have tophysically drive off the road and onto a non-road in order to leave theroute at almost any point, a fewer number of points can be used todefine the route. Points provided at actual turns 401, 407 are stillused, as well as two points 403, 405 to define the curved portion of theroad. If a large enough threshold were employed, even points 403 and 405would not be needed.

In this illustrative embodiment, as more options become available foroff-route conditions, the threshold is dynamically lowered. For examplebetween points 407 and 413, the threshold is lowered close to theoriginal threshold shown in FIG. 3. In this embodiment, this is due tothe fact that several exits are possible where the user could go offroute, and accordingly it is desirable to determine an off-routecondition more quickly (e.g., use a smaller threshold). For example, ifthe larger threshold were used, then the system may not even detect anoff-route condition at point 319.

Even with this reduced threshold over this portion of the highway, thesystem is able to draw out the route using only turn points 409 and 411.

It is desirable to strike a balance between a maximum threshold (toreduce required route points, thus reducing the data size of the entireroute) and a minimum time to detect an off-route condition. This can beachieved, for example, without limitation, by dynamically adjusting thethreshold based on a number of options for off-route conditions or bydynamically adjusting the threshold based on a road classification type.

In one system of classification, roads are given a rating based on thespeed limit of the road. The classification can generally define classesof road (e.g., without limitation, a class III road may have a speed of40-50 mph). Although not a perfect guide, roads with speeds of over 60mph are generally highways (and thus usually have fewer off-routeoptions than, for example, a surface street). Accordingly, in oneembodiment, the system will use a larger threshold when the driver istraveling on a highway class road and a smaller threshold when thedriver is on a surface road.

The surface roads may even be further delineated between classes, suchthat classes that commonly have less space between them or more exitsare mapped with smaller thresholds than are roads that common are morespaced apart or have less exit opportunities.

In yet a further embodiment, one or two general thresholds may be used.For example, a threshold of one hundred feet may be used for highwaytravel and a threshold of twenty feet may be used for surface roadtravel.

Particular methods of adjusting thresholds can be used based on the needfor balancing speed of calculation vs. size of download vs. delay inoff-route calculation. For example, using the simple two-thresholdmethod would produce faster results and keep a relatively small sizedtotal route in many cases, since the large threshold on highways willoften produce a route with few data points connecting long distances.This system, however, could be more susceptible to slower diagnosis ofoff-route conditions, and there is greater chance for a user to travelfurther off-route before being notified of the error than under anothersystem.

Using a greater number of threshold delineations, with at least onebelow twenty feet (as an example) could reduce the likelihood of delayin diagnosing an off-route condition, but could increase the number oftotal route points needed to define a route. This would increase theoverall download size. The processing time may also be increased, ascalculating more points may take a longer time.

In a third example, the threshold size may be dynamically determinedbased on the number of off-route options for an upcoming stretch of aroute. In this embodiment, the processing time would likely be increasedbecause the system would have to “check” a portion of a route foroff-route options (e.g., without limitation, count the number ofturn-offs). The number of data points would likely be more than thefixed two threshold system as well, and the resulting data package wouldlikely be larger. The off-route notification, however, would likely becloser to an optimal situation, since the threshold is lowered when ahigher number of off-route possibilities are present.

FIG. 5 shows an illustrative example of a process for adjusting athreshold based on a road classification. In this embodiment, a routedetermination process examines a segment of a route to be traveled 501.Although the route could be divided in numerous manners, in thisembodiment, a segment is defined by each individual road. In otherwords, when a route calls for a driver to leave one road for another, anew segment is obtained. A threshold corresponding to the segmentclassification is set 503, and then the process checks to see if anyfurther segments exist 505. If no new segments exist, the processproceeds to route calculation 507. If segments remain, the process movesto a next segment 509 and repeats the threshold setting.

Any evaluation process, including, but not limited to, that shown inFIGS. 5, 6, and 7, may also be performed for a portion of a long route.The process may be subsequently then repeated as a next portion of theroute is approached.

For example, in a route running from Detroit to Los Angeles, a routedetermination process may first be performed for a stretch of roadrunning from Detroit to Chicago (or a smaller or larger portion of theroute). Since the driver will not need information past Chicago for atleast a few hours (the amount of time it takes to drive from Detroit toChicago), a very large threshold can be used to approximate the routefrom Chicago to Los Angeles. Alternatively, the entire route can beexamined and downloaded at the onset using a detailed threshold level.

As the driver approaches Chicago (or at any point after the initialdirections have been delivered to get the driver on the way), the systemcan then evaluate a second portion of the route. In this manner, a routecan be quickly evaluated, and more precise directions can be obtained asthey are required. This is yet another example of providing a bandwidthefficient route, which may have a high degree of accuracy with regardsto off-route reporting yet is still deliverable in a rapid manner over alow bandwidth connection.

If the system is only verbally providing directions, as opposed todisplaying the entire route (or some future portion of the route), thendirections can be calculated at some predetermined time before they areneeded, such that a higher degree of accuracy can be used with respectto the threshold whilst maintaining a concise and rapid delivery.

FIG. 6 shows an illustrative example of a process for dynamicallyadjusting an off-route threshold based on a likelihood of an off-routeoccurrence. In this illustrative embodiment, the system again evaluatesa segment of a route 601. It is possible to divide the route intosegments based on when a turn is made, as with the example provided withrespect to FIG. 5. In this embodiment, however, the road is divided intosegments of predetermined length. If a segment is shorter than thepredetermined length, it is simply treated as its own segment.

Although not necessary, by dividing the segment into predeterminedlengths, a better trade-off between efficiency and off-route detectionmay be obtained. For example, if a twenty mile stretch of road had fiveexits within the first five miles, and no exits for the next fifteenmiles, treating the entire road as one segment might result in a lowthreshold (due to the number of exits at the onset). Dividing the roadinto four five-mile segments (as one non-limiting example) could resultin a first evaluation using a low threshold, but subsequent evaluationsusing a much greater threshold and thus potentially requiring fewer datapoints. Of course, it is also contemplated that the road will be dividedbased on turns (such that the entire exemplary twenty mile segment wouldbe evaluated as a single segment).

After selecting a segment for evaluation 601, the system determines alikelihood an off-route occurrence 603. This could be based on, forexample, a number of exits, a road class, etc. One example of such adetermination is shown with respect to FIG. 7.

Based on the likelihood of the off-route occurrence, a threshold is setfor that segment of the route 605. The system then determines whether ornot any segments of the route remain 607. If no segments remain, thesystem proceeds to route determination 609. Otherwise, the systemselects a next segment 611 and continues with threshold setting.

FIG. 7 shows an illustrative example of a process for determining alikelihood of an off-route occurrence 603. In this illustrativeembodiment, the determination is based on a number of opportunities foran off-route occurrence.

In this embodiment, a segment is evaluated 701 until an exit point isreached 703 or a segment ends 707. If an exit point is reached, acounter is incremented 705. If the segment has not yet ended 707, theprocess continues.

If the segment has ended, the process can proceed to assigning athreshold 605.

The navigational route and threshold processing described above may beperformed at CPU 3 at vehicle 31 (FIG. 1). Alternatively, processing maybe performed at one or more computer servers in communication withnetwork 61. As explained above, data may be communicated between CPU 3at vehicle 3 and the server(s) via wireless communication links 14/55(using nomadic device (ND) 53) or link 20 (using modem 63).

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

1-6. (canceled)
 7. A navigation method comprising: determining a routeto a destination; determining a road classification for each road or aportion of each road comprising the route; assigning a tolerance to eachroad or portion of each road based on the determined classification forthat road or road portion; using the assigned tolerances, determiningpoints defining the route such that the roads comprising the route arewithin a bounded area defined by the tolerance in conjunction with aplurality of lines connecting successive points along the route; anddelivering the determined points to a vehicle computing system incommunication with a server.
 8. The method of claim 7, wherein thebounded area is an area having the lines as a central axis and thetolerance defines a distance to either side of the lines, betweensuccessive points, to an outer border of the bounded area.
 9. The methodof claim 7, wherein the bounded area is an area having the line as acentral axis and the tolerance defines a distance, axially centeredabout the lines, such that half the tolerance equals the distance fromthe line to an outer border of the bounded area.
 10. The method of claim7, wherein the higher speed limit of a road or portion of a road is, asindicated by the classification, the higher the tolerance assigned tothe road is. 11-23. (canceled)
 24. A system comprising: a server inwireless communication with a vehicle computing system, configured to:determine a destination route; divide the route into a plurality ofportions; determine a road classification for the portions; assign atolerance to each portion based on the classification; using theassigned tolerances, determine route points such that the roadscomprising the route are within a bounded area; and deliver thedetermined points for navigating the vehicle toward the destination. 25.The system of claim 24, wherein the bounded area is an area having thelines as a central axis and the tolerance defines a distance to eitherside of the lines, between successive points, to an outer border of thebounded area.
 26. The system of claim 24, wherein the bounded area is anarea having the line as a central axis and the tolerance defines adistance, axially centered about the lines, such that half the toleranceequals the distance from the line to an outer border of the boundedarea.
 27. The system of claim 24, wherein a higher speed limit of a roador portion of a road is, as indicated by the classification, the higherthe tolerance assigned to the road is.
 28. A computer readable storagemedium storing instructions which, when executed by a processor, causethe processor to perform the method comprising: determining a route to adestination; determining a road classification for each road or aportion of each road comprising the route; assigning a tolerance to eachroad or portion of each road based on the determined classification forthat road or road portion; using the assigned tolerances, determiningpoints defining the route such that the roads comprising the route arewithin a bounded area defined by the tolerance in conjunction with aplurality of lines connecting successive points along the route; anddelivering the determined points to a vehicle computing system incommunication with a server.
 29. The computer readable storage medium ofclaim 28, wherein the bounded area is an area having the lines as acentral axis and the tolerance defines a distance to either side of thelines, between successive points, to an outer border of the boundedarea.
 30. The computer readable storage medium of claim 28, wherein thebounded area is an area having the line as a central axis and thetolerance defines a distance, axially centered about the lines, suchthat half the tolerance equals the distance from the line to an outerborder of the bounded area.
 31. The computer readable storage medium ofclaim 28, wherein the higher speed limit of a road or portion of a roadis, as indicated by the classification, the higher the toleranceassigned to the road is.